1. Field of the Invention
The present invention relates to an integrated circuit arrangement for setting a predefined phase difference between a first and second high-frequency signal. The invention relates furthermore to an integrated circuit having a circuit arrangement of this type.
2. Description of the Background Art
The invention is within the field of integrated circuits (IC) in which high-frequency signals are transmitted with a fixed phase relation. The invention is in particular within the field of integrated high-frequency front-end circuits, with whose help a high-frequency (HF) incoming signal in transmitting/receiving devices of communication systems, such as, e.g., a radio signal in the gigahertz range received over an antenna, is converted into a quadrature signal with a fixed, low frequency (intermediate frequency, IF), before the signal is demodulated and the data values contained therein, originating from another transmitting/receiving device, are detected.
Prior-art integrated HF front-end circuits have a low-noise amplifier (LNA) and a quadrature-mixer for spectral down conversion of the amplified signal. To derive the quadrature signal, the quadrature mixer, also called an image reject mixer, contains two mixers, controlled by two local oscillator signals, phase-shifted by 90 degrees relative to one another. In the case of such local oscillator signals (and in other signals of the HF front-end circuit), these are usually differential signals whose components have a phase difference of 180 degrees. To reduce feedback effects of the mixer on the local oscillator, the mixer and the local oscillator are typically placed at a relatively large distance from the integrated circuit.
Because of technology or process variations and/or because of design asymmetries, deviations from the ideal phase offset of 90 or 180 degrees may occur, which may greatly impair the efficiency of the HF front-end circuit. In prior-art receivers, such phase deviations in the intermediate frequency or baseband range are compensated by multiplying, e.g., a digitalized quadrature signal with a complex-valued factor in such a way that the desired phase offset of 90 or 180 degrees is restored.
The calibration circuits, e.g., based on switchable resistance networks, require chip area. In addition, the calibration range, i.e., the maximum deviation from the ideal phase offset that can be corrected in this way, is relatively small and the precision (resolution) of the phase correction relatively low. The necessary phase relation can be set in a relatively narrow band in this way.